Device for gas-exit ducts to convert vortical gas flow to sound-attenuated axial gas flow

ABSTRACT

High intensity sound generated as a result of venting a vortical gas flow via a gas-exit duct is attenuated by the described gasflow straightening device comprising a generally frustum-shaped tube having a conical or frustum-shaped inner member attached to the inner tube surface by several axially mounted flow-aligning vanes; the device being adapted to align with and sealably engage the gas-exit duct.

United States Patent 1191 Kunz, Jr. May 20, 1975 [54] DEVICE FOR GAS-EXIT DUCTS T0 2,671,523 3/1954 Walker 181/49 CONVERT VORTICAL GAS FLOW To 3,130,812 4/1964 HllbtiCll 181/60 X SOUND-ATTENUATED AXIAL GAS FLOW FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Walter George Kunz, Jr., 213,734 2/1958 Australia l8l/49 Wilmington, Del. [73] Assignee. E I du Pom de Nemours & Primary Examiner-Richard B. Wilkinson l Assistant ExaminerJohn F. Gonzales Company wllmmgton Attorney, Agent, or Firm.lames A. Costello [22] Filed: July 11, 1974 [21] Appl. N0.: 487,782 [57] ABSTRACT High intensity sound generated as a result of venting a 52 us. c1. 181/41; 181/49; l8l/7O vertical gas flow via a gas-exit duct is attenuated y 51 1111. C1. FOln 1/00 the described gas-flow straightening device comprising [58] Field of Search 181/41, 47 R, 47 A, 47 B, a generally fruswm-shaped tube having a conical of [81/49 60, 70 33 HB frustum-shaped inner member attached to the inner 1 tube surface by several axially mounted flow-aligning 561 References Ci vanes; the device being adapted to align with and sealengage the gas-exit duct.

1,685,701 9/1928 Blanchard 181/70 X 7 Claims, 8 Drawing Figures r r v T l4 g) 20 H A I8 50 W PATENTEB HAYZOIQYS SHEET 2 OF 2 FIG.6

DEVICE FOR GAS-EXIT DUCTS TO CONVERT VORTICAL GAS FLOW TO SOUND-ATTENUATED AXIAL GAS FLOW BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns a sound attenuation device for converting vortical gas flow from a gas-exit duct to reduced-velocity axial gas flow.

2. Description of the Prior Art The prior art is silent concerning the structural design of the device described herein. Although conical diffusers are known, and straightening vanes are known, their combination in the relationship taught herein has heretofore not been appreciated. See Cyclone Dust Collectors, Engineering Report Prepared for American Petroleum Institute, Feb. I, 1955, American Petroleum Industry, New York City, pages 28 and 29.

The combination of conical diffuser/vanes that is described herein provides first for slowing a vortical gas flow by the use of the diffuser and then for changing the gas flow to axial flow. Surprisingly, the device described herein has been found to attenuate gas exit duct noise to a significant degree.

The noise-reducing device of this invention is useful on any kind of apparatus in which a gas exits from a duct in a vortical flow which upon release produces audible sound. The invention device is operable with variable gas flow rates. A vortical flow can result, for instance, at the gas exit ducts of an apparatus designed to centrifugally separate dispersed material from a gas.

The invention is especially applicable to centrifugal separators commonly known as cyclones, particularly cyclones incorporated in traps used to remove leadcontaining solids from exhaust gas of internal combustion engines. Such cyclone separators are well-known in the art. Typical cylcone separators include those decribed in Fluid and Particle Mechanics, by C. E. Lapple, University of Delaware, on pages 305-309; and those disclosed in Chemical Engineering Practice, Cremer and Davies, Academic Press, Inc., New York (1957) on page 466.

With regard to employment of the device of this invention upon the gas exit duct of, say, a cyclone separator. the benefits achieved can be understood as follows. The use of a spreading annulus to slow the gas flow is important to minimize back pressure. Attempts to eliminate the whistle merely by incorporating axially aligned vanes inside the throat of cyclone gas exit ducts are not entirely satisfactory. The vanes substantially increase the pressure drop. In exhaust gas solids traps, increased pressure drop would mean increased back pressure against the engine and would result in reduced engine performance and fuel economy. The device described herein provides for reduced noise without substantial pressure drop, resulting in practically no sacrifice of engine performance or fuel economy to achieve sound attenuation.

SUMMARY OF THE INVENTION This invention concerns a device for attenuating the sound that results from releasing a vortical gas flow from the opening of a gas exit duct, the device comprising i. a frustum-shaped tube open at both ends one of which is narrower than the other, the narrow end being adapted to sealably and smoothly engage the opening (throat) of the gas exit duct in axial align ment with the duct,

ii. a cone-shaped inner core having one end wider than the other, positioned within tube (i) to form an annulus between the tube and the core, the wide end of the core being in the direction of the wide end of the tube,

iii. an outer body open at both ends having one end axially united to the wide end of tube (i), the outer body extending along the tube axis to provide a gas flow defining wall, the open end away from the end that is united to tube (i) having an inside diameter at least equal to the diameter of the end that is united to the tube,

iv. an inner body coaxial with and united to core (ii) having an outer diameter at least equal to the diameter of the core at the place of union, said inner body extending along the tube axis to provides a gas flow defining wall, said inner body and said outer body defining a second annulus in communication with the first annulus, said inner body and core (ii) combination being closed to gas flow therethrough,

v. a multiplicity of vanes across the annulus defined by the inner and outer bodies, each vane disposed axially along the tube and having a length effective to convert vortical gas flow to axial gas flow.

The expression cone-shaped inner core must be understood to include both cone-shaped inner cores and frustum-shaped inner cores. The expression is used for simplicity and is generic to both types of inner cores, e.g. those of FIGS. 1 and 3. The device of this in vention contemplates an inner core that has an outer surface diameter nearest (e.g. at or below) the narrow end of tube (i) that is from 0.2 to 0.8 times the diameter of the narrow end of tube (i).

The term upper in the following description refers to the location furthest from the gas exit duct. The device of this invention contemplates that the diameter of the wide end of tube (i) is 1.5 to 4.0 times the diameter of the narrow end and preferably 1.6 to 2.5. It has been found that values of at least 1.5 and preferably 1.6 give excellent results in slowing down vortical flow and preparing the gas flow for contact with the straightening vanes.

Also contemplated are the embodiment wherein: l the outer body and the inner body are each generally cylindrical (see FIG. 1); (2) the outer body and inner body increase in diameter as they extend beyond their union with tube and core respectively (see FIG. 6), (3) the inner body has attached at its wider end, or upper end if the inner body is generally cylindical, (as a means for spreading axial gas flow) a circular plate across the tube axis; the plate will have at least the diameter of the outer body at its upper edge and will be positioned away from the edge, clearing it by at least the distance between the edge and the nearest surface of the inner body (see (FIGS. 7 and 8); and (4) the inner body extends above the upper edge of the outer body furthest from the tube union (see FIGS. 7 and 8).

In FIGS. 7 and 8 the extension of the inner body need not have the gas flow spreader combined therewith. Note also that the extension need not have the same dimensional relationship between its lower and upper ends as does the inner body. For instance, FIG. 8 shows a generally cylindrical inner body and an extension in which the diameter increases as the distance increases away from union with the inner body.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section along the axis of an embodiment of this invention adapted to fit upon a vortical gas flow duct.

FIG. 2 is an axial end view of the embodiment sectioned in FIG. 3.

FIG. 3 is a section along the axis of an embodiment of this invention.

FIG. 4 is an axial end view of the embodiment sectioned in FIG. 5.

FIG. 5 is a section along the axis of an embodiment of this invention.

FIG. 6, FIG. 7 and FIG. 8 are sections along the axes of other embodiments of this invention.

In all of the Figures that show the invention in section, the device is depicted in relation to the gas flow duct to which it is appended. The duct, however, forms no part of this invention.

DETAILS OF THE INVENTION FIG. 1 illustrates one embodiment of this invention having axially aligned frustum-shaped tube 12, inner core 16, outer body 14, inner body 18, and radial vanes 20 spanning the distance between bodies 14 and 18. FIG. 1 also shows the relationship among various parameters which govern a change in gas flow velocity, direction and type (vortical to axial).

The narrow end of tube 12, corresponding in diameter to throat 44, (diameter A is smoothly united with gas-exit duct 10 which is attached to a structure (not shown) from which gases exit via said duct 10. The diameter of core 16 at throat 44, marked B is 0.2 to 0.8, preferably 0.4 to 0.6, times throat diameter A. The angle, a, of the inner surface of tube 12 is to 70, preferably 20 to 50. Angular spread or exceeds angular spread ,8 of the surface of core 16 by 0 to 40, preferably 0 to 20. The angles are determined by extending sides 12 (for a) and sides 16 (for B) to intersect in a conical point at which point the angle is measured. The opening at the wide end of tube 12, marked C, is 1.5 to 4.0, preferably 1.6 to 2.5, times A.

Core 16 extends from below throat 44 to plane 50 across the axis of tube 12. As shown, it can be a complete cone w hich extends into duct 10 to a point past throat 44. However, variations in later figures show that it can be a frustum of a cone so long as it occupies or extends below throat 44. Conical first annulus 46 extends from peripheral space in throat 44 to space between core 16 and tube 12 at plane 50.

Second anhulus 48 (see FIG. 2) is formed between inner body 18 and outer body 14, extends annulus 46 through plane 50 and provides a flowpath in which gas can be passed between vanes 20. Inner surface of body 14 is smoothly united with inner surface of tube 12. Outer surface of inner body 18 is smoothly united with outer surface of core 16. The united inner body and core is always closed to communication between its ends, preferably at the narrow end of the core. When the narrow end is at the duct throat, closure must be there. The second annulus can be conical, that is, be formed between surfaces whose radius increases with extension, or can be cylindrical, that is, formed between surfaces of radii which do not change with extension.

Vanes 20 positioned between bodies 14 and 18 begin at or above plane 50, at or above where annulus 46 ends. They extend along the axis and are coextensive with inner body 18 and outer body 14 and are effective to redirect gas flow from the first annulus toward axial flow. Their effective axial lengths, i.e., axial lengths (marked H on the Figure) along which they bridge across the second annulus, are 0.l to 4.0, preferably 0.5 to 1.5, times the diameter of throat 44. The vanes normally number 4 to 20, preferably 8 to 16. Vanes need not be symmetrically placed and too many, as well as too few, diminish the effectiveness of sound attenua tion.

With reference to FIG. 1, the device operates in this way upon vortical gas flow: gas passes through duct 10 in tight spirals that follow the interior duct peripheries. At throat 44 (wherein expansion of the gas flow crosssectional area begins) the gas loses vortical velocity as it moves through annulus 46 in the annular passageways of increasing diameter and area. As the gas loses vortical velocity, it loses its predominantly rotational direction around the duct axis, and acquires a direction in closer alignment with the duct axis. Gas from annulus 46 flows through annulus 48 past vanes 20 which divert the gas to directions even more aligned with the duct axis. The so-aligned gas flow has a greatly reduced tendency to produce high intensity noise, especially high frequency whistles.

FIG. 2 and associated FIG. 3 illustrate an embodiment of the device which differs from FIG. 1 in that its tapered core is not pointed. Core 52 has closure 51 at throat 44.

FIG. 4 and associated FIG. 5 illustrate a gas flow straightening embodiment which differs from that of FIG. 2 in that its core 53 extends below throat 44. Core 53 is open inside duct 10 but is closed to communication through inner body 18 by closure 54.

FIG. 6 illustrates an embodiment having conical core 16 extending into outlet duct 10 below throat 44. Tube 12 is extended along vanes 60 as conically spreading outer body 62. Core 16 is extended along vanes 60 as conically spreading inner body 61.

The embodiment of FIG. 7 has conical core 16 ex tended along vanes 64 as conically spreading inner body 61. Tube 12 is extended along vanes 64 as conically spreading outer body 65 terminating at edge 67. Vanes 64 extend through the annulus between body 65 to its edge 67 and body 61. Vanes 64 extend further to join with coaxial circular plate 66 across the tube axis. Plate 66 is attached to body 61 and has at least the diameter of body 65 at edge 67. Its periphery clears edge 67 by at least as much as does body 61. Such a design enables this embodiment to be positioned inside a chamber where little clearance exists for gas converted to axial flow.

FIG. 8 shows another embodiment of this invention which can accommodate small clearances beyond its outlet end. In addition to the basic structure described for FIG. 1, it has support frustum 70. Frustum 70 has an angular spread through the axis, marked 0, of 20 to preferably 40 to 60. Coaxial circular plate 71 extends across the end of frustum 70. It clears edge 69 of body 14 by at least as much as body 18 clears the edge 69. Plate 71 has at least the diameter of body 14 at edge 69.

These devices can be made of any suitable material which resists the temperature and forces of gas from the gas exit ducts. The material should resist sound generation. The devices can be fabricated by any suitable combination of techniques adapted to produce finished devices, such as casting, machining, bending, fitting and uniting. Parts can be united by snap fits or adhesion methods, such as by welding, or they can be held in alignment by exterior holders so as to maintain their integrity during use.

Any one or more of elements (i), (ii), (iii), (iv) and (v) as defined herein can be joined to the gas exit duct or to the apparatus from which the duct extends; or, any one or more of the elements can be joined to other instrumentalities such as a wall of an enclosure that may partially surround the exit opening of the device of this invention. Those skilled in the art may conceive of other ways in which to keep the elements of this invention in cooperating relationship without departing from the scope of this disclosure.

The devices of this invention can be adapted to have a slip fit over a gas exit duct. In any event, they should smoothly continue the exit duct internal surface into the inner surface of the frustum-shaped tube.

Sound Attenuation Sound attenuation was demonstrated employing a device as shown in FIG. 1 fixed over the outer end of the gas exit duct ofa cyclone separator (having an axial vane type inlet) such as described in the Chemical Engineering Practice" volume for which the citation is given above. It is noted that cyclone separators form no part of the instant invention and are referred to merely as examples of one type of apparatus in which the invention device can be effectively employed.

The union of the inside of the tube depicted in FIG. 1 (having the same inner diameter as the exit duct) with the exit duct was smooth. Eight vanes, each parallel to the cone axis and symmetrically spaced in the cylindrical annulus, were used. With reference to FIG. 1, the parameters in this structure were a 35; ,8 28; B 0.6A; C 1.67A; and H 0.53A.

A closed chamber was sealed to the cyclone solids discharge opening. The cyclone was mounted in a chamber so that its axial inlet vanes communicated with a surrounding chamber of constant flow compressed air while its gas exit was vented to the atmosphere. A pressure gauge was attached to the inlet line to the surrounding chamber.

A constant flow rate of air was established through the surrounding chamber while the cyclone exhausted the air through the gas exit duct with the attached device. At that air flow, the chamber pressure was 34.5 psig.

The sound emitted during air flow was analyzed with a General Radio Company, Model I558BP, noise analyzer by measuring sound amplitudes at discriminated frequencies to determine decibel (db) ratings at those frequencies.

The cyclone was similarly tested without the device of this invention, using the same constant air flow rate. The chamber pressure was 34.5 psig in that test too. Comparative sound amplitudes in decibels, with and without the invention device, are shown in the Table below against selected frequencies. The All cycles" frequency refers to frequency over the 31 .5l6,000 cps range.

TABLE Amplitudes (in decibels) Frequency With Flow Without Flow (Cycles/second) Straightener Straightener All cycles 105.5 I I6 16,000 89 90 8.000 97.5 99 4,000 98 98 2,000 I00 103 L000 10] I I6 500 9L5 l00 250 86.5 86 I25 82 63 77.5 82 31.5 83 86 These values demonstrate the significant sound attenuation achieved by use of the device of this invention. It should be noted that a 15 decibel improvement was effected at 1,000 cycles per second which is one of the frequencies most objectionable to the human ear. This degree of attenuation is readily appreciated by the human ear.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. The device for attenuating sound that results from releasing a vortical gas flow from the opening of a gas exit duct, the device comprising i. a frustum-shaped tube open at both ends one of which is narrower than the other, the narrow end being adapted to sealably and smoothly engage the opening of the gas exit duct in axial alignment with the duct,

ii. a cone-shaped inner core having one end wider than the other, positioned withinn tube (i) to form a first annulus between the tube and the core, the wide end of the core being in the direction of the wide end of the tube,

iii. an outer body open at both ends having one end axially united to the wide end of tube (i), the outer body extending along the tube axis to provide a gas flow defining wall, the open end away from the end that is united to tube (i) having an inside diameter at least equal to the diameter of the end that is united to the tube,

iv. an inner body coaxial with and united to core (ii) having an outer diameter at least equal to the diameter of the core at the place of union, said inner body extending along the tube axis to provide a gas flow defining a second annulus in communication with the first annulus, said inner body and core (ii) combination being closed to gas flow therethrough,

v. a multiplicity of vanes axially disposed across the annulus defined by the inner and outer bodies having lengths effective to convert vortical gas flow to axial gas flow.

2. The device according to claim 1 wherein the inner core has an outer surface diameter nearest the narrow end of tube (i) that is from 0.2 to 0.8 times the diameter of the narrow end of the tube and the opening at the wide end of the tube is 1.5 to 4.0 times the opening at the narrow end.

3. The device according to claim 2 wherein the outer surface diameter of the inner core nearest the narrow end of tube (i) is from 0.4 to 0.6 times the diameter of the narrow end of the tube, and the opening at the wide end of the tube is 1.6 to 2.5 times the'opening at the narrow end.

4. The device according to claim 1 wherein the outer body and the inner body are each generally cylindrical.

5. The device according to claim 1 wherein the outer body and inner body increase in diameter as they extend beyond their union with tube and core, respectively.

6. The device according to claim 1 wherein a circular body extends above the upper edge of the outer body. l

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN PATENT NO. 1 3,884,325 DATED May 20, 1975 INVENTOR(S) Walter George Kunz, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"flow defining" said inner body Signed and Sealed this twenty-ninth Day Of July 1975 [SEAL] A lies I:

RUTH C. MASON Arresting Officer C. MARSHALL DANN ('ummissinm'r uflarents and Trademarks UNETE STATES PATENT ()FFICE CERTIFMATE @F 21'? EUHUN PATENT NO. 3,88%323 DATED May 20, 1975 |NVENTOR(S) Walter George Kunz, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

At column 6, Claim l(iv) line 51, after "flow defining" and before "a. secand annulus insert wall, said inner body and said outer body defining Signed and Sealed this twenty-ninth Day Of July 1975 [SEAL] A nest:

RUTH' C. Me'SON C. MARSHALL DANN Arresting ()jjrcer ('mnmissiunvr nflulenrs and Trademarks 

1. The device for attenuating sound that results from releasing a vortical gas flow from the opening of a gas exit duct, the device comprising i. a frustum-shaped tube open at both ends one of which is narrower than the other, the narrow end being adapted to sealably and smoothly engage the opening of the gas exit duct in axial alignment with the duct, ii. a cone-shaped inner core having one end wider than the other, positioned withinn tube (i) to form a first annulus between the tube and the core, the wide end of the core being in the direction of the wide end of the tube, iii. an outer body open at both ends having one end axially united to the wide end of tube (i), the outer body extending along the tube axis to provide a gas flow defining wall, the open end away from the end that is united to tube (i) having an inside diameter at least equal to the diameter of the end that is united to the tube, iv. an inner body coaxial with and united to core (ii) having an outer diameter at least equal to the diameter of the core at the place of union, said inner body extending along the tube axis to provide a gas flow defining a second annulus in communication with the first annulus, said inner body and core (ii) combination being closed to gas flow therethrough, v. a multiplicity of vanes axially disposed across the annulus defined by the inner and outer bodies having lengths effective to convert vortical gas flow to axial gas flow.
 2. The device according to claim 1 wherein the inner core has an outer surface diameter nearest the narrow end of tube (i) that is from 0.2 to 0.8 times the diameter of the narrow end of the tube and the opening at the wide end of the tube is 1.5 to 4.0 times the opening at the narrow end.
 3. The device according to claim 2 wherein the outer surface diameter of the inner core nearest the narrow end of tube (i) is from 0.4 to 0.6 times the diameter of the narrow end of the tube, and the opening at the wide end of the tube is 1.6 to 2.5 times the opening at the narrow end.
 4. The device according to claim 1 wherein the outer body and the inner body are each generally cylindrical.
 5. The device according to claim 1 wherein the outer body and inner body increase in diameter as they extend beyond their union with tube and core, respectively.
 6. The device according to claim 1 wherein a circular plate is attached to the inner body at its upper end, the plate being disposed cross-axially, and having a diameter at least that of the outer body at its upper edge, the plate being positioned away from the edge and clearing it by at least the distance between the edge and the nearest surface of the inner body.
 7. The device according to claim 1 wherein the inner body extends above the upper edge of the outer body. 